Bale was so unrecognizable that co-star Robert De Niro had to ask who Bale was upon meeting him on set.

It's not the first role Bale has gained or lost weight for — "The Machinist," the "Dark Knight" trilogy, and recent film "Out of the Furnace" all required dramatic changes in his appearance.

While Bale may be a master of transformation, he's certainly not the only Hollywood actor who has gone above and beyond — losing weight, undergoing hours of makeup application, and wearing prosthetics — for a role.

"There were some nights that I thought I literally was going to die," Portman told EW. "It was the first time I understood how you could get so wrapped up in a role that it could sort of take you down."

Christian Bale lost more than 63 lbs. for his role in "The Machinist."

Getty/Paramount

Bale got down to a body weight of 120 pounds by running, and on a daily diet of an apple and can of tuna.

The actor gained it all back, plus an extra 30 pounds, for his role as Bruce Wayne in "Batman Begins."

"... I think putting weight on, unfortunately I had to put it on pretty fast and it's not very healthy doing that. That was when I felt bad. I did actually start to feel I was putting my body under too much pressure because I put on 100 pounds in five months."

Robert De Niro changed his body type twice for one film.

Screenshot/ United Artists

Talk about dedication.

In order to play the iconic boxer Jake LaMotta in "Raging Bull," Robert De Niro built muscle and trained with the legend himself to get the look of the boxer during his heyday. De Niro even fought in three different boxing matches in attempt to be as convincing as possible.

To portray LaMotta's later years, De Niro packed on almost 60 pounds of weight, a drastic body change that gave the actor rashes and breathing issues.

It paid off — De Niro picked up both a Golden Globe and Academy Award for his role in "Raging Bull."

George Clooney ditched his clean-shaven appearance for an award-winning part in "Syriana."

Featureflash/ Shutterstock.com, Warner Brothers

In order to play the role of CIA Agent Bob Barnes in the oil/political thriller "Syriana," Clooney gained over 35 pounds, grew a bushy beard, and shaved back his hairline to look just right.

"There was nothing fun about it," said Clooney. "There was not a moment that was fun about shooting this film. That's not a slap on the film or (the director Stephen) Gaghan. It's just that everybody has that year where you age a decade and this was that one for me."

Rooney Mara received several facial piercings and shaved her head to play "The Girl with the Dragon Tattoo."

Getty/Columbia Pictures

Here's a way to make a first leading-role impression.

In order to play the goth-hacker Lisbeth Salander, Rooney Mara ditched her delicate appearance, piercing her eyebrow, nose, and lip, dying her hair raven black, chopping her bangs, and even shaving part of her head.

But Leto took it a bit too far. His dramatic weight gain caused him serious health issues resulting in him landing in a wheelchair.

"Toward the end of the shoot, one of the glaring issues was the pain I had with my feet," Leto told the NY Daily News. "I couldn't walk for long distances; I had a wheelchair because it was so painful. My body was in shock from the amount of weight I gained."

Charlize Theron gained 30 pounds for her Oscar-winning role in "Monster."

"Monster" writer-director Patty Jenkins spoke to CNN about Theron's transformation, saying it was less about making Theron "fat and ugly" and more about the little things.

"Yeah, just shocking because it was little details. It was, 'Oh, she was homeless. She lived on the street in bad weather. OK, well that means sun damage.' Well, then we addressed the sun damage. She was insecure about her hair, OK, well, then we address the hair. It was little little layers and then suddenly she's Aileen," Jenkins said.

Tom Hanks spent a year losing weight for "Cast Away."

Associated Press/20th Century Fox

Film production took a one-year hiatus so Hanks could diet for his role as a FedEx employee who ends up stranded on a deserted island. He dropped more than 50 pounds and grew a frighteningly long beard to achieve an authentic shipwrecked look.

This isn't the first time Hanks has gone above and beyond for a movie. He lost 30 pounds to play AIDS-patient turned plaintiff in the drama, "Philadelphia."

Hanks recently revealed he has type 2 diabetes because of his weight gain and loss over the years.

Cate Blanchett played legend Bob Dylan in "I'm Not There."

Getty/The Weinstein Company

Blanchett was one of the six actors to portray legendary rocker Bob Dylan in the 2007 biopic, and as the only female of those six, Blanchett had her work cut out for her.

Blanchett, who says she's one to accept challenges, told People, "I just strapped those breasts down and went for it."

John Travolta donned a fat suit and fake Baltimore accent in "Hairspray."

Getty/New Line Cinema

Travolta donned a 30-pound fat suit and underwent five hours of makeup preparation a day to play the supportive, stay-at-home mother of Tracy.

It wasn't easy, Travolta said, mentioning he even got some advice from another fat suit-familiar actor.

“There's an added level of weight to carry around, but more than that it was very hot inside,” revealed Travolta. “Martin Lawrence had warned me that it was not going to be easy, and others had warned me it was not going to be easy. So I was sweating a lot. A lot of air [was] needed. High heels were difficult to dance in but I committed to [it].”

Hilary Swank spent weeks physically and mentally preparing for a transgendered role in "Boys Don't Cry."

Associated Press/Fox Searchlight

In the late 1990s, Hilary Swank was relatively unknown in the film industry. That quickly changed when she took on the role of a transgendered teen, Brandon, in 1999's "Boys Don't Cry."

To prepare, Swank not only spent weeks researching and reading novels on transgender people, she lived as a male for a month, cutting off her hair, and strapping down her chest.

"I could have come in and asked to let the stunt woman do the obstacle course," Moore says. "But I felt I would have walked away having missed an opportunity experiencing, first-hand, what these people actually go through in training; it's the whole reason for doing this film in the first place."

And we can't forget Moore's iconic hair change — the actress actually buzzed off all her hair for the role.

Ben Kingsley shaved his head and lost 20 pounds to play Gandhi.

Director Sir Richard Attenborough had been searching for an actor to play Gandhi for 20 years when he offered British actor Ben Kingsley the role.

Kingsley, whose father is of Indian descent, underwent extensive preparation for the role — reading biographies, studying photographs, shaving his head, and losing 20 pounds on Gandhi's very own vegetarian diet.

''When I have totally immersed myself in the mechanical, logical preparation of a part, if I and my craft are totally bonded and fully exploited, something else in me is awakened and begins to inform my work..."

Matt Damon gained more than a few pounds for his role in 2009's "The Informant!"

Getty/The Informant

For his role as a whistle blower, Damon sported a comb-over, mustache, nose appendage ... and oh yeah, an extra 30 pounds.

"At my age, all I had to do to gain weight was eat the way I did when I was in college and the weight went on instantly," he told the Daily News. "It was a little horrifying."

Cameron Diaz underwent a major hair change for "Being John Malkovich."

Associated Press/USA Films

For her role as Lotte, eccentric wife of John Cuscak's character, Craig, in "Being John Malkovich," Diaz said goodbye to her naturally straight blonde hair and red carpet gowns for a dark frizzy wig and some rather unflattering get-ups.

"I didn't realize that people weren't going to recognize me until I put the costume on and I stood around talking to people working the production," Diaz told CrankyCritic. "I just assumed they knew it was me, but they thought I was a stranger."

Dustin Hoffman played a woman in "Tootsie."

"... I went home and started crying," he says in the AFI interview. "Talking to my wife, I said, 'I have to make this picture,' and she said, 'Why?' And I said, 'Because I think I am an interesting woman when I look at myself on screen. And I know that if I met myself at a party, I would never talk to that character because she doesn't fulfill physically the demands that we're brought up to think women have to have in order to ask them out.'"

Gwyneth Paltrow wore a fat suit in "Shallow Hall."

Getty/20th Century Fox

To transform into an overweight woman in the Jack Black comedy, Paltrow wore a 25-pound fat suit to film the movie.

"The first day I tried [the fat suit] on, I was in the Tribeca Grand [hotel in New York City] and I walked through the lobby. It was so sad; it was so disturbing. No one would make eye contact with me because I was obese."

Tom Cruise wore a fat suit and prosthetics to play Les Grossman in "Tropic Thunder."

Cruise is nearly unrecognizable as character Les Grossman, an overweight, middle-aged, and extremely potty-mouthed businessman.

For the role, Cruise donned a fat suit, large prosthetic hands, chest hair wig, and a bald cap.

Cruise wasn't the only one in "Tropic Thunder" to alter his appearance. Robert Downey Jr.'s wore blackface.

Getty/Red Hour Films

Downey Jr. received some backlash for playing Kirk Lazarus, a white Australian actor who has his skin surgically dyed to take on the movie role of an African-American sergeant.

He discussed the moment Ben Stiller approached him about the role on CBS saying it was the "stupidest idea" he ever heard.

"I thought in the right context it could be entertaining or it could be disastrous. But there's that thing of the risk factor for any creative idea," said Downey Jr. "Nowadays it's just very, very convenient to pick things apart ... I remember coming up watching comedies like this ... things that were really off-kilter and really largely in poor taste but there was something about the brand name of the people who were directing ... and someone said, 'You know what, we know that they have a moral psychology.'"

John Hurt wore prosthetics to channel a deformed Joseph Merrick in "The Elephant Man."

The 1980 drama film "The Elephant Man" tells the true story of Joseph Merrick, a severely deformed man from 19th century London, and John Hurt's transformation into Merrick is perhaps one of the most convincing in film history.

The depiction was so effective it inspired the creation of an Academy Award for best makeup. But, with such an intense costume, Hurt had to revise his eating and resting schedule.

"I would have my last meal at midmorning, at a stage in the makeup when I could use a straw," Hurt told the Los Angeles Times. "I usually had two raw eggs mixed in orange juice. After that I had nothing till I got home ... That was usually around midnight, because it took an hour and a half to take the makeup off."

Daniel Day-Lewis put a year of preparation into his role of Abraham Lincoln.

To prepare for his role as the former president, Day-Lewis spent a year reading and thinking about Lincoln — through photos, novels, and biographies. He also practiced and perfected Lincoln's high-pitched voice, using it in-between takes and even after filming concluded.

“Without sounding unhinged, I know I’m not Abraham Lincoln. I’m aware of that. But the truth is the entire game is about creating an illusion, and for whatever reason, and mad as it may sound, some part of me can allow myself to believe for a period for time without questioning, and that’s the trick.”

To get into the part of Harry Potter's arch nemesis, British actor Ralph Fiennes shaved his head every day, wore false fingernails, dentures and fake reptilian skin, and underwent almost three hours of make-up application.

Fiennes told The Hollywood Reporter that his look was so convincing, one kid burst into tears upon seeing him on set.

"I felt very good about myself," Fiennes said. "Children should be really scared of Lord Voldemort."

Eddie Murphy wore a foam and prosthetic suit for "The Nutty Professor."

Eddie Murphy's transformation in the "The Nutty Professor" was so good that it won the film an Academy Award for Best Makeup.

Murphy played seven characters, including Professor Sherman Klump, all of whom were created using latex molds of Murphy's face. The actor also donned a fat suit made of polyurethane and spandex, oversized rubber hands, and latex bladders (for a jiggle effect).

Rebecca Romijn wore hundreds of plastic scales in "X-Men."

Eight hours. The amount of time it took to apply silicone scales to Rebecca Romijn's body for her role as Mystique in "X-Men."

Things got a bit easier by the time the sequel came around, though.

"We've got it down – we did it the other day in three-and-a-half hours, as opposed to the ten hours it was in the beginning. On the last movie, we never did it under eight hours," she told IGN. "It took eight hours, every single day, to put that costume on, and they've changed a whole bunch of things – the fumes don't make me sick anymore, it's much more comfortable, it's easier to take off, and we can do it in three-and-a-half hours ... Regular hair and make-up takes two hours ..."